FIELD OF THE INVENTION
The invention relates to a superconducting toroidal magnet system.
In electrical power technology, the question of the extent to which superconducting magnet systems are suitable at appropriate cost for storing electrical energy has been the subject of recent investigation. Such systems are also known by the abbreviation SMES (Superconducting Magnetic Energy Store).
A superconducting energy store or accumulator is known, for instance, from European Patent 0 348 465 B1. The current store or accumulator shown therein has a toroidal coil system with many subcoils. The various subcoils or coil segments can be selectively connected in series or parallel and can be connected to a supply device for charging or discharging the entire configuration. It is also provided that for charging, for instance, only some of the coil segments are connected together. The interconnection of the coil segments can also be different for charging and for discharging. It is also possible for the energy store or accumulator to be loaded with a series circuit of some of the coil segments or all of the coil segments, and to discharge it in a parallel circuit.
In such superconducting magnet systems, what is known as a quench situation can arise, which can be considered a structural problem. In it, the superconduction is interrupted at one point in the superconductor by an excessive temperature increase.
The tripping event may be a very small local release of energy, which leads to a temperature increase of only a few degrees. However, since the superconductor is normally conductive, that is highly resistive, above its so-called transition temperature, the electrical current must be absorbed by so-called stabilizing material, for example highly conductive copper into which the superconductor is embedded. That leads to further local heating due to so-called Joulean losses, the heat spreads, and the normally conducting zone grows.
Unless countermeasures were taken, that process would not end until all of the energy inductively stored in the magnet of the system was dissipated. When large amounts of energy are stored, the temperature in the hot zone ("hot spot") could become so high as to cause destruction of the magnet.
In order to overcome that problem, either as much energy as possible can be extracted (case a), or the heated zone in the magnet system can be increased spatially, so that the resultant maximum temperature is not as high (case b).
In case a, when there are large quantities of energy stored, a limitation exists through the use of the discharge voltage (because P=U.times.I!). The higher the voltage, the faster the energy can be extracted. The lower it is, the lower the maximum temperature which is then attained.
In case b, further quenching locations must be created in the magnet system. That can be carried out, for instance, by externally supplied quench heaters. However, the safety of the magnet system in the quench situation, after quenching is detected, depends on the tripping and functional reliability of the quench heaters. After that so-called secondary quench is created, the entire coil system may finally have to be run down until cold before operation can be resumed. Until then, the coil system is unavailable.
U.S. Pat. No. 5,146,383 discloses a superconducting magnetic energy storing system in which a plurality of magnet systems are divided into two groups. Each of the two groups has an associated supply device. A device for mutual takeover of current between the groups is provided. The magnet systems of the various groups are connected electrically in series.